A concrete slab can look dry and still hold enough moisture to cause flooring problems.
The warning signs often appear after installation. Vinyl flooring begins to lift, adhesive bonds weaken, or an epoxy coating develops blisters. Fixing the damage may involve removing the failed material, investigating the slab, and preparing the surface again.
Concrete moisture testing helps contractors identify these risks before installing moisture-sensitive flooring or coatings.
Two established methods are ASTM F2170 and ASTM F1869. One measures relative humidity inside the concrete. The other measures moisture vapor leaving its surface.
Although both methods assess moisture conditions, they produce different results. The correct choice depends on the flooring manufacturer’s requirements, the slab, and the project specifications.
Here’s what contractors need to know before testing begins.
What Is the Calcium Chloride Test (ASTM F1869)?
ASTM F1869 measures the moisture vapor emission rate (MVER) from a concrete floor.
The result indicates how much moisture vapor leaves the slab’s surface during a specified period. Technicians report it in pounds per 1,000 square feet over 24 hours.
The test uses anhydrous calcium chloride, a material that absorbs moisture.
A technician prepares a clean section of bare concrete and places a preweighed calcium chloride dish on the surface. An airtight dome seals the dish over the test area.
After 60 to 72 hours, the technician removes and weighs the dish again. The increase in weight provides the information needed to calculate the moisture vapor emission rate.
What Does ASTM F1869 Tell You?
The calcium chloride test measures moisture vapor released at the concrete surface under the conditions present during testing.
It remains useful when a flooring manufacturer specifies an allowable MVER value.
However, it does not measure the relative humidity deeper inside the slab.
Temperature, ambient humidity, surface condition, and preparation can influence results. For this reason, technicians must follow the environmental and testing requirements of the applicable standard.
ASTM F1869 is not intended for gypsum concrete or concrete containing lightweight aggregate. Existing coatings and other surface materials must also be addressed according to the testing procedure.
What Is the Relative Humidity Test (ASTM F2170)?
ASTM F2170 measures relative humidity within a concrete slab using in-situ probes.
Rather than collecting moisture vapor at the surface, technicians drill holes to specified depths and install sensors that measure internal conditions.
The required depth depends on how the concrete dries.
For a slab drying from one side, technicians typically position the measurement point at 40% of the slab thickness.
For concrete drying from both sides, they use a depth of 20%.
After preparing the holes and installing the probes, technicians allow the required equilibration period before taking readings. ASTM F2170 generally requires at least 24 hours.
Results are reported as a percentage of relative humidity (RH).
Why Is Internal RH Testing Useful?
Moisture does not distribute evenly throughout a concrete slab.
The surface may dry faster than the material beneath it. Once an impermeable flooring system covers the concrete, moisture can redistribute within the slab.
ASTM F2170 provides information about internal moisture conditions that surface emission testing cannot directly measure.
Many flooring and coating manufacturers use RH limits when establishing installation requirements.
However, probe readings still depend on correct placement, calibration, testing conditions, and documentation.
A reading from one location does not automatically represent the entire floor.
ASTM F2170 vs F1869: What’s the Difference?
The main distinction is straightforward: ASTM F2170 measures internal relative humidity, while ASTM F1869 measures surface moisture vapor emission.
| Testing factor | ASTM F2170 | ASTM F1869 |
| Measurement | Relative humidity inside concrete | Moisture vapor emitted from the surface |
| Method | In-situ probes | Calcium chloride dishes |
| Result | Percentage RH | lb/1,000 sq. ft./24 hours |
| Typical test period | Minimum 24-hour probe equilibration | 60–72-hour exposure |
| Test location | Specified depth within the slab | Prepared concrete surface |
| Main consideration | Correct depth and probe installation | Surface and environmental conditions |
| Acceptance limit | Flooring manufacturer’s RH limit | Flooring manufacturer’s MVER limit |
These measurements are not interchangeable.
For example, an internal RH result of 85% cannot be converted into a reliable calcium chloride emission rate.
Each test examines a different moisture condition, so contractors must compare the readings with the manufacturer’s specifications for that particular method.
Which Concrete Moisture Test Should You Use?
Start with the flooring or coating manufacturer’s installation instructions.
Some systems require ASTM F2170. Others specify ASTM F1869 or allow both methods under defined conditions.
If the manufacturer sets an internal relative humidity limit, use the approved RH testing procedure.
If the specification requires an MVER result, the calcium chloride method may be appropriate, provided the slab meets the standard’s requirements.
The concrete itself can affect the decision.
For example, ASTM F1869 is unsuitable for lightweight aggregate concrete. Contractors must identify an accepted alternative rather than applying an incompatible test.
Avoid relying on a universal moisture threshold.
Moisture readings are only one part of evaluating a concrete floor. Facility managers should also understand the signs your warehouse floor needs moisture mitigation and investigate visible problems before selecting a flooring system.
One adhesive may tolerate higher moisture levels than another. A coating system may also have different requirements from resilient flooring.
The applicable limits should come from the exact products selected for the project.
What Happens When Concrete Moisture Levels Are Too High?
Excessive moisture can interfere with the bond between concrete and certain flooring materials.
The resulting damage depends on the products installed, the substrate, and the moisture conditions.
Common problems include adhesive failure, coating blisters, floor covering distortion, and discoloration.
Moisture-related problems can also affect epoxy floor coatings, particularly when slab conditions exceed the coating system’s moisture limits. Testing before installation helps contractors identify risks and determine the appropriate next steps.
For commercial facilities, repairs can create additional costs and operational disruption.
Warehouses, manufacturing spaces, and retail properties may need to restrict access while damaged flooring is removed and replaced.
Testing helps identify potential problems before installation, but an elevated reading does not automatically mean the entire floor needs a moisture mitigation system.
The result must be evaluated against the specified flooring requirements.
When Is Concrete Moisture Mitigation Necessary?
Moisture testing and moisture mitigation serve different purposes.
Testing establishes the moisture conditions within or at the surface of a slab.
Mitigation addresses moisture conditions that exceed the requirements of the planned flooring or coating system.
If the test results fall within the manufacturer’s acceptable limits, additional mitigation may not be necessary.
When results exceed those limits, the project team must determine an appropriate response.
Depending on the flooring system and site conditions, this may involve additional drying time, a compatible moisture mitigation system, or a change in the specified materials.
The selected approach must follow the relevant manufacturer’s instructions.
At All West Surface Prep, the team uses in-situ relative humidity testing to assess concrete moisture conditions. When necessary, the company evaluates and installs moisture mitigation systems based on the project requirements.
Learn more about its concrete moisture testing and mitigation services.
Why Surface Preparation Still Matters
Passing a moisture test does not guarantee that a new floor will bond correctly.
Adhesives and coatings also depend on the condition of the concrete surface.
Old adhesives, contaminants, curing compounds, weak surface material, and unsuitable concrete profiles can interfere with installation.
Contractors must address these issues separately from moisture testing.
For example, grinding or shot blasting may be necessary to remove existing materials and create the surface profile required by the new flooring system.
However, surface preparation should follow the intended installation and testing procedures. Aggressive grinding immediately before a moisture test can affect surface conditions, particularly when using the calcium chloride method.
All West Surface Prep provides commercial concrete surface preparation, including grinding, shot blasting, and substrate profiling for flooring and coatings.
Proper testing and preparation help establish a more reliable starting point for installation.
Frequently Asked Questions
1. How long does concrete moisture testing take?
ASTM F1869 typically requires a 60- to 72-hour test period.
ASTM F2170 requires at least 24 hours of equilibration before valid probe readings can be taken.
Both methods may require additional time for site conditioning, preparation, equipment setup, and reporting.
2. Why is concrete moisture testing important before flooring installation?
Excess moisture can contribute to adhesive failure, bubbling, discoloration, and other flooring problems.
Testing helps contractors determine whether slab conditions meet the requirements of the intended flooring or coating system.
It also provides documented readings for project records.
3. Can ASTM F2170 and ASTM F1869 be used on the same project?
Yes, if both methods are suitable for the concrete and permitted by the project requirements.
Some projects specify both tests to obtain information about internal humidity and surface moisture vapor emission.
However, results cannot be directly converted or treated as equivalent.
4. What happens if flooring is installed over concrete with excessive moisture?
Moisture-related problems may include adhesive breakdown, blistering, lifting, curling, and discoloration.
The type and severity of damage depend on the flooring material, installation conditions, and moisture exposure.
Repairs may require removing damaged materials, investigating the moisture source, and preparing the substrate for a suitable replacement system.
5. How many concrete moisture tests are required?
ASTM F2170 and F1869 commonly specify three test locations for the first 1,000 square feet, followed by one additional test for each additional 1,000 square feet.
Using that schedule, a 10,000-square-foot floor requires at least 12 tests.
Always confirm the current applicable standard and project specifications, since additional locations may be necessary.
6. What is an acceptable moisture level for a concrete slab?
There is no universal acceptable moisture level for every floor.
The maximum RH or MVER depends on the flooring product, adhesive, coating, and manufacturer requirements.
A moisture reading that meets one product’s limits may exceed another’s.
Use the technical specifications for the system being installed to determine whether the slab is ready.
7. Does every concrete slab need moisture mitigation?
No.
Testing may show that the slab already meets the manufacturer’s moisture requirements.
If readings exceed acceptable limits, the contractor should evaluate options before proceeding.
The goal is to address a documented moisture issue, not install a mitigation system unnecessarily.
Test Before You Install
A dry-looking concrete surface does not confirm that the slab is ready for moisture-sensitive flooring.
ASTM F2170 and ASTM F1869 provide different measurements, and each has a place when project specifications call for it.
Choosing the correct method, documenting results, and evaluating the concrete before installation can help reduce the risk of flooring failures and costly rework.
All West Surface Prep provides concrete moisture testing and mitigation for commercial and industrial flooring projects. The team uses in-situ RH testing to evaluate slab conditions and determine whether mitigation is required.
Contact All West Surface Prep to discuss your slab, flooring specifications, and project requirements before installation begins.